Variable length blade

ABSTRACT

A variable length blade in telescopic form adapted to be used with comparable blades to form a variable diameter rotor or propeller and wherein the outer blade portion is caused to telescope with respect to the inner blade portion by jackscrew action and wherein the outer blade portion is connected to the jackscrew by a plurality of tension-torsion straps extending between the outer blade portion and a series of nuts on the jackscrew.

United States Patent 1191 Fradenburgh 1 Oct. 30, 1973 [5 VARIABLE LENGTHBLADE 3,128,829 4 1964 Young 416/88 [75] Inventor: Evan AlbernFradenburgh, FOREIGN PATENTS OR APPLICATIONS Falffield, Con". 252,4615/1926 Great Britain 416/87 [73] Assignee: United Aircraft Corporation,East H tf d Conn Primary ExaminerSamuel Feinberg Att0rneyVernon F.I-Iauschild [22] Filed: Sept. 18, 1969 Appl. No.: 859,094

US. Cl. 416/89 1 [51] Int. Cl B63h1/06.- [58] FieldofSearch ..4l6/147,88, 87, 416/89; 74/424.8, 841,459

[56] References Cited UNITED STATES PATENTS 2,163,482 6/1939 Cameron..416/ss 2,659,241 11/1953 1161mm ..74 /424 s [57] ABSTRACT A variablelength blade in telescopic form adapted to be used with comparableblades to form a variable diameter rotor or propeller and wherein theouter blade portion is caused to telescope with respect to the innerblade portion by jackscrew action and wherein the outer blade portion isconnected to the jackscrew by a plurality of tension-torsion strapsextending between the outer blade portion and a series of nuts on the vjackscrew.

23 Claims, 17 Drawing Figures Patented 0a. 30, 1973' v 3,768,923

I 5 Sheets-Shoot 1 FIGJ I A 'IIIIIIIIIIIIIIII/ Patented Oct. 30, 1973 5Shegts-Sheet 7:

Patented Oct. 30, 1913 3,768,923

Patnted 0a.. 30, 1973 5 Shoots-Shoot 5 FIGJB 1,

1 VARIABLE LENGTH BLADE CROSS-REFERENCE TO RELATED APPLICATIONS Thisapplication teaches a blade construction of the type generally disclosedin and usable with the system disclosed in copending application Ser.No. 759,287 filed Sept. 12, 1968, on Mechanism For Synchronously VaryingThe Diameter Of A Plurality Of Rotors And For Limiting The Diameters byEvan A. Fradenburgh.

BACKGROUND OF THE INVENTION 1. Field of Invention A This inventionrelates to variable length blades adapted to be used in variablediameter rotors or propellers of the aircraft type and which consists ofa telescoping blade actuated by a jackscrew arrangement wherein theouter blade portion is connected to the jackscrew through a plurality oftension-torsion straps, which constitute a soft spring in connecting theouter blade portion to a plurality of nuts on the jackscrew so as toaccomplish equal nut and nut thread loading under centrifugal load ofthe rotor in flight and so as to permit the blade to vary in pitchwithout causing the nuts to move on the jackscrew.

2. Description of the Prior Art In the variable diameter rotor art,blades of telescopic construction have been caused to vary in length andhence vary the diameter of the rotor by means of a jackscrew mechanism.One such construction is shown in Cameron U. S. Pat. Nos. 2,163,481 and2,163,482 but this construction did not anticipate high centrifugalloading of the blading during the time of blade length variation inflight, nor did they anticipate the need to accommodate continual pitchchange, such as modern helicopters experience due to cyclic pitchvariation. In the Cameron construction a stiff tube connects a singlenut on the jackscrew to the outer telescoping blade portion, and whilesuch a construction was probably adequate at that time since Cameronsrotor rotates at relatively low speeds and the blades are not subject tocyclic pitch variation, modern helicopters having high tip speeds andhigh stress levels require extensive design improvements in this area.To accommodate such design considerations utilizing the Cameronconstruction, an extremely long nut coacting with the jackscrew shaftwould be needed and it would be impossible with such a long nut toachieve equal loaddistribution across the various threads of the nutsince the elastic deformation which occurs in the parts being joinedthrough the nut causes the end threads to be extremely heavily loadedwhile the intermediate threads are virtually load-free. Such loading, ofcourse, causes excessive wear in the end threads and, in an extremecase, this loading of the end threads could cause failure of thosethreads, thereby throwing the load on the next adjacent threads topropagate progressive thread failure in rapid succession so that the nutwould be free to slide off of the jackscrew, thereby releasing the outerblade portion.

If a short nut were to be considered for use, its threads and thejackscrew would have to be extremely large and heavy. Such size andweight requirements render usage prohibitive.

In addition, modern helicopters require almost continual cyclic pitchchange of their blades, and the rigid tube of Cameron would thereforecause his single large nut to be continuously moving on the jackscrewshaft, thereby establishing an intolerable wear and heat generatingsituation, as well as undesirable radial in and out movements of theouter blade portions in an assymetrical rotor head pattern.

In the past, attempts have been made to achieve equal nut thread loadingin a single nut construction of the type taught in Cameron by placing alapping compound on the threads and loading the threads under asimulated centrifugal force and then letting the nut threads wear or lapthemselves in to the point where each is equally loaded. This threadlap-in procedure is not successful because the heavy centrifugal loadingplaced on the threads during blade extension and retraction causestemperature buildup and resultant thermal deformation of the threads sothat the carefully lapped-in and load equalizing thread clearances arelost due to this thermal deformation and the unequal thread loadingsituation reoccurs. In addition, this thread lapin solution producesthread load equalization only at the specific centrifugal load conditionat which the lapping-in occurred.

Accordingly, since the centrifugal load on the blade varies in flight, asingle thread load equalization condition is of no great assistance.

U. S. Pat. No. 3,128,829 shows a telescoping blade construction verysimilar to the aforementioned Cameron patents and it will be evidentthat it includes the same operational limitations.

SUMMARY OF INVENTION A primary object of the present invention is toprovide a variable length blade utilizing a jackscrew and nutarrangement to produce telescopic motion between inner and outer bladeportions and wherein the threads of the nut arrangement are equallyloaded and blade diameter is unaffected by blade pitch variation.

In accordance with the present invention, a plurality of short nuts areplaced on the jackscrew and individually connected to the outer bladeportion by tensiontorsion straps. The use of a plurality of nutsintroduces the requirement that the individual straps connecting thenuts to the blade tip distribute equal loading to each nut. In thisinvention such straps are of sufficient length and physicalcharacteristics with respect to the nuts that they form a soft springrelative to the nut threads during blade centrifugal loading. The changein tension-torsion strap length by elastic stretching under tensionloading caused by blade centrifugal loads is very large compared topossible changes in thread spacing. Accordingly, each nut will carry itsproportional share of the total centrifugal load within a smallpercentage, and this equal nut thread load carrying capability willoccur at all significant load levels.

In accordance with a further aspect of the present invention, due to thetorsional mobility and flexibility of these elongated tension-torsionstraps, the blade outer portion can change pitch, collectively orcyclically,

without imparting motion to the nuts on the jackscrew I shaft.

The invention provides structural redundancy by utilizing a plurality ofthin tension-torsion straps between several nuts and the outer bladeportion as opposed to a single connection between a single nut and theouter blade portion.

In accordance with a further aspect of the present invention, the nutsof the jackscrew-nut arrangement may be of the wing nut variety with thetension-torsion straps connected to opposite wings of each nut, and suchnuts may be identical and staggered slightly to permit eachtension-torsion strap to pass clear of all other straps, and these nutsmay be pinned to prevent relative rotation therebetween, with the pinaxis parallel to the screw axis so as to allow freedom of relative axialdisplacement required to insure equal nut loading. Since the jackscrewthreads will elongate due to blade loading, and since the elongationwill vary over the length of the jackscrew where the nuts are attached,freedom of axial displacement between the nuts is required and suchpinning permits this axial displacement. i I

In accordance with a further aspect of the present invention, the nutsof the jackscrew arrangement can be of the same size and in alignment,with tension-torsion strap passing through a drilled passage in its ownattachment nut and clearing through all other nuts on the blade tip sidethereof, and wherein said tension-torsion straps are retained in saidnuts and in a plate member at the blade tip by bolt head and nutengagement and other conventional means.

In accordance with still a further aspect of the present invention, boththe nuts and the inner blade member are made of elongated cross-sectionso that the nuts have a limited degree of rotational freedom withrespect to the inner blade member before bearing positively thereaginstin positive stop fashion.

In accordance with another aspect of this invention, positive stops areprovided to limit the amount of telescoping motion of the outer blademember on the inner blade member.

In accordance with a further aspect of this invention, both the innerblade member and the outer blade member are mounted together for pitchchange motion about the blade feathering axis.

In accordance with still a further aspect of this invention, bearingblocks are provided to support the outer blade member for telescopingaction on the inner blade member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial showing, partiallybroken away, of a variable diameter rotor or propeller of a modernaircraft, such as a helicopter, illustrating my invention.

FIG. 2 is a top view, partially broken away, illustrating my inventionused in a variable length rotor blade.

FIG. 3 is a showing through line 3-3 of FIG. 2.

FIG. 4 is a showing taken along line 4-4 of FIG. 2.

FIG. 5 is a showing taken along line 5-5 of FIG. 2.

FIGS. 5a and 5b are partial showings similar to FIG. 5 showing the nutmember at the opposite ends of relative rotation travel with respect tothe blade.

FIG. 6 is a partial showing,- partially broken away, of a variablelength blade utilizing a preferredembodiment of my invention.

FIGS. 7 and 8 illustrate segmented nuts of the wing nut variety on ajackscrew and receiving tensiontorsion straps to illustrate anotherembodiment of my invention.

FIG. 9 is a schematic representation of a single, elongated nut on ajackscrew.

FIG. 10 is a graphic representation of thread loading on the nut of FIG.9.

9 Wing nut. FIGS. 13 and 15 are a top view and an end view,respectively, and FIG. 14 is a section along line 14-14 of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 we see thevariable area blade in the environment of a variable diameter rotor 10,which may be used on a modern helicopter. Rotor 10 could also be apropeller for a fixed wing aircraft. Rotor 10 consists of a plurality ofequally spaced blades 12 projecting from rotor hub 14 for rotationtherewith about rotor axis of rotation 16.

Blades 12 are appropriately supported, for example by stack bearings(not shown), for pitch change motion about blade feathering axis 26 sothat the blades may change pitch both collectively and cyclically.Blades 12 may be of the type more fully described in U. S. Pat. No.2,163,482.

Swash plate assembly 30, which may be of the type more fully disclosedin U. S. Pat. No. 2,925,130, is sup ported from spherical bearing 32 andstandpipe 34, which project from the housing of the transmission unit24. Blade pitch controls 36, which are conventional and may be of thetype fully disclosed in U. 5. Pat. No. 3,199,601, are utilized to causethe swash plate assembly 30 to translate along axis 16 and act throughpivotal pitch change rod 38 and pitch change horn 40 to cause the pitchof blades 12 to vary collectively. Control 36 can also cause swash plateassembly 30 to tilt with respect to axis 16 and thereby cause the pitchof the blades to vary cyclically in conventional fashion. This cyclicpitch variation occurs throughout the rotation of blades 12.

Rotor 10 is supported from fuselage or wing 18 and is driven by engine20 through reduction gear 22 and transmission 24. Engine 20 may be ofthe type shown in U. S. Pat. Nos. 2,711,631 and 2,747,367, and reductiongears 22 may be of the type shown in U. S. Pat. No. 2,91 1,851. While arigid rotor is shown, the invention is equally applicable to anarticulated rotor of the type shown in U. S. Pat. No. 2,925,130, so longas a universal joint (not shown) is placed in jackscrew shaft 66.

Engine 20 drives transmission input drive shaft 42, which carries bevelgear 44 at one end thereof. Bevel gear 44 coacts with and drives bevelgear 48, which is connected to and drives rotor drive shaft 51 tothereby cause rotor 10 to rotate about axis of rotation 16.

We shall now consider the mechanism which causes rotor 10 to changediameter. Stillviewing FIG. 1, we see that shafts 50 and 52 arepositioned coaxially by appropriate support bearings (not shown), aboutaxis 16 and each carries at one end thereof bevel gears 54 and 56,respectively, which form part of differential 58, which also includespinion gears and 62 so that there is one such pinion gear for each blade12 in rotor 10. These pinion gears 60 and 62 connect directly tojackscrew or jackscrew shaft 66 in each blade 12.

As engine 20 causes rotor 10 to rotate about axis 16, shafts 50 and 52will rotate therewith. Each of the shafts 50 and 52 has a clutch orbrake member 70 and 72 connected thereto. Both of these brakes are pilotoperated in conventional fashion, for example, through a solenoidmechanism. When brake 70 is applied, shaft 50 and bevel gear 54 arestopped and, as rotor drive shaft 51 and hub 14 continue to rotate, thepinions such as 60 and 62 will be caused to rotate and thereby rotatejackscrews 66. Nut assembly 100, which will be described in greaterparticularity hereinafter, threadably engages jackscrew shaft 66 and isfree to move therealong feathering axis 26 within a chamber 102 definedbetween jackscrew 66 and inner blade portion or torque tube 104 of blade12. Nut assembly 100 is connected to outer movable blade portion 106through a plurality of tension-torsion strap members indicated in FIG. 1generally as 110 so that translation of nut assembly 100 away from rotorhub 14 will permit centrifugal force to cause outer blade portion 106 totelescope outwardly with respect to inner blade portion 104, therebyincreasing the diameter of rotor 10, and so that translation of nutassembly 100 inwardly will act through tension-torsion straps 110 tocause outer blade member 106 to telescopeinwardly toward hub 14 withrespect to inner blade member 104, thereby reducing the diameter ofrotor 10. Application of retraction brake 72 will cause blade 12 toretract and thereby reduce in length and rotor to decrease in diameter,while application of extension brake 70 will cause blade 12 to extendand thereby increase in length and rotor 10 to increase in diameter. Itwill be evident that the pitch and hand of the threads of jackscrew 66and nut assembly 100 determines the rate of diameter change of rotor 10and whether the diameter will increase or decrease.

Referring to FIGS. 2-5, we see a preferred embodiment of my variablelength blade 12. Outer blade portion 106 is of airfoil cross-section andinner blade or torque tube portion 104 is of elongated cross-section,such as elliptical cross-section. Outer blade portion 106 consists ofspar portion 108 and trailing edge portion 111. Blade tip cap 112 fitsoverthe outer end of outer blade portion 106 to provide a properlyshaped aerodynamic tip therefor. Spar bearing blocks 114 and 116 attachto spar 108 as shown in FIG. 3, by any convenient means such as screwmembers 120. Tu'be bearing blocks 122 and 124 attach to blade innerportion 104 by any convenientmeans such as bolt mechanisms 126 and 128(See FIG. 4). Spar bearing blocks 114 and 116 and tube bearing blocks122 and 124 coact to guide outer blade portion 106 in its telescopingmotion inwardly and outwardly with respect to inner blade portion 104. i

To cause outer blade portion 106 to translate with respect to innerblade portion 104, jackscrew 66 is caused to rotate in one direction orthe other by the mechanism disclosed and described in connection withFIG. 1, and thereby cause nut assembly 100 to translate therealong andalong feathering axis 26. Nut assembly or segmented nut 100 includes aplurality of individual nuts or nut segments 100a, 100b, 100C, l00c, and100e as shown in FIG. 2. At least one tension-torsion strap extends fromeach opposite side of each of nuts 100a--l00e and connects to the tipportion of outer blade portion 106 in a fashion to be described ingreater particularity hereinafter.

By viewing FIG. 2 it will be noted that during blade retraction,adjustable positive stop members 130 and 132 abut tube bearing blocks122 and 124 in positive one of the primary load path members; that is,the jackscrew or straps.

As best shown in FIG. 5, nut assembly is of elongated shape along theblade chord axis 134 and is smaller in size than the inner wall of tubemember 104, thereby permitting limited relative rotation of nut assembly100 within innner tube or blade member 104 about axis 26. The elongatednut shape allows sufficient relative freedom between the nut and tubesuch that pitch change motions of the blade will not cause the nut torotate on the jackscrew and to extend or retract the blade. If the nutwere of the same shape and size as the inner wall of the tube, thecyclic pitch inputs would turn the nut and cause an undesirable andassymetric cyclic variation in blade length. Such cyclic relativeoscillation between the nut and jackscrew would also result in anintolerable lubrication and wear problem. Since the spar bearing blocks1 l4 and 116 provide rigidity to the tube 104, and since the nutassembly 100 and these blocks move radially inwardly and outwardlytogether, it is preferable to align the nut assembly 100 under thebearing block 114 and 116 to provide extra tube stiffness as the nutsurfaces bear against the inner wall of the tube during extension orretraction. Other than this slight limited relative motion of the nutand tube, the nut is restrained from further relative motion by itscontact with the tube inner wall, such that jackscrew rotation willdrive the nut axially to draw the outer blade portion inward or allow itto extend outward so shown in FIGS. 5a and 5b. The nut external surfaces109, 111, 113, and 115 are contoured to the contour of the inner surface117 of the tube 104 so as to provide full surface contact when extensionor retraction is to be made rather than line or point contact. Dependentupon the allowable stress consideration, the shape of the nut may betrapezoidal, triangular, or of other shape, so long as its sides makecontact with the inner wall of the blade inner portion after apredetermined amount of relative motion has been completed. A preferredembodiment of my invention is shown in FIG. 6, wherein outer bladeportion 106 is caused to telescopically move with respect to inner bladeportion 104 along feathering axis 26, in a fashion now to be described.Individual nuts 100a-100e threadably engage jackscrew 66 and will betranslated therealong in response to jackscrew rotation. Tension-torsionstraps extend between nuts 100a-100e and the tip of outer blade portion106 where theyengage plate member 140, which attaches to outer blademember by any convenient means such as screws 142 and 144.

Tension-torsion straps 1 10 may be of any shape, such as a flat shape ormay actually be circular in crosssection, and may be connected to nuts100a-100e and outer blade member 106 in any preferred manner offastening such as by threaded members, staking, snap rings, or the like.In the FIG. 6 construction the tension-torsion straps 110are of the wireor rod type and of circular cross-section and extend through drilledholes in nuts 100a-l00e and plate member 140. Two strapsattach to eachnut and pass through aligned clearance holes provided as required in theadjacent nuts. As shown in FIG. 6 rods 110a and 110b, 110a and 110d,l10e and 110f, 100 and llOh, 110i and 110j, connect nuts 100a, 100b,100c, 100d, and 1002, respectively, to plate 140 in blade outer portion106. Each rod, such as 110a, passes through aligned apertures, such as146, 158, 160, 162, and 164 in the nuts. The rods may have both heads,such as 150, at one end thereof, and nuts, such as 152, threadablyengaging the opposite end thereof. It will be noted that the alignedholes for each strap clearance are offset from all other sets of alignedholes, thereby offsetting all straps.

In order to provide outer support for the jackscrew 66, bearing support125 is installed at its outer radial end as shown in FIG. 4. Recessesscrew fasteners 127 connect the bearing support to blade inner portion104.

In operation, as nuts la-100e are caused to trans late on jackshaft 66,outer blade portion 106 moves in telescopic fashion with respect toinner blade portion 104 because each of nuts 100a-l00e is individuallyconnected to the tip 112 of outer blade portion 106 throughtension-torsion straps 110a-110j. These nuts and the threads therewithinwill be substantially equally loaded due to blade centrifugal forceduring rotor operation. Tension-torsion straps 110a-110j constitute asoft spring with respect to nuts 100a-100e so that the straps willdeform under centrifugal load and the nuts l00a-l00e will be loadedsubstantially equally. This result is achieved due to the extensivelength of tensiontorsion straps 110a-110j as opposed to the height ofnuts l00a-100e. We accordingly see that by the elongation of straps 1due to tension loading by the blade centrifugal force, nut loadequalization is accomplished. In addition, due to the length andtorsional flexibility of straps 110, blade outer portion 106 can vary inpitch without imparting rotational motion to nuts l00al00e, since straps110 will twist around feathering axis 26 during blade pitch changebefore friction forces on the nuts are overcome. As mentionedheretofore, it is necessary that the nut assembly be of sufficientlysmaller size and selected shape to allow the blades to change pitchwithout contacting the nuts.

FIGS. 7 and 8 show another modification of my multi-nut unit 100,wherein wing nuts 200, 202, 204, and

206 threadably engage jackscrew 66 and individual tension torsion straps110k, 110l, 110m, and l10n extend from wings 208, 210, 212, and 214thereof. It will be understood that similar tension-torsion strapsproject from the corresponding wings (not shown) on the opposite side ofwing nuts 200-206. It will be noted in the FIG. 7-8 construction thattension-torsion straps 110 are of flat stock and are retained in wings208-241 by receipt of their bulbous ends in enlarged recesses in thewings. It will be further noted that the wings 208-241 of nuts 200-206are slightly spaced angularly to avoid tension-torsion strapinterference.

Pins 209, 211, and 213 extend between adjacent nuts 200-206 in adirection parallel to axis 26, so as to prevent relative rotationbetween the nuts while permitting simultaneous translation of all nutsalong jackshaft 66 during rotor diameter varying operation and to allowrelative axialv displacement between the nuts as required to insureequal nut loading. This axial freedom is provided so that non-uniformthreads or screws which are due to manufacturing variations, elasticstrains, or thermal expansion because of frictional heat duringoperation of the screw, will not cause one nut to pick up load at theexpense of the other.

'justment means (that is, nut ends) may Referring to FIGS. 13-15 we seeanother method of attaching tension-torsion straps 110 to one of thesegmented nuts 200. While one strap only is shown connected to one ofthe wings 208 of wing nut 200, it should be borne in mind that a strapis similarly attached to the opposite wing of nut 200 and to the wingsof all of the other nuts, for example, as illustrated in FIGS. 7 and 8.It will be noted that in the FIG. l3l5 construction, tension-torsionstrap 110 is of flat stock and is connected to wing 208 by bolt members,such as 300 and 302, which pass through holes in the end of strap 11 0and are threadably received in threaded apertures, such as 304,'in wing208. It will further be noted that ear 208 is contoured as best shown inFIG. 14 so that the straps from the various nuts may be closely spacedin the assembly and not required to be separated by the height of thehead of bolts 300 and 302. Close spacing is required because of thelimited space available within the blade tube confines and the need foran angular degree of freedom between nuts and tube. The opposite end ofstrap 110 is connected to the tip of blade 12 in any convenient fashion.

The advantage to be gained by the multiple nut construction taughtherein over the single elongated nut construction of the prior art, suchas the Cameron patent, is made clear by viewing FIGS. 9 and 11 withtheir attendant thread load charts shown in FIGS. 10 and 12. FIG. 9illustrates an elongated single nut member 220 on jackscrew 66 and byviewing FIG. 10, it will be noted that, due to elastic deformation ofthe nut and jackscrew, the end threads are heavily loaded, while theintermediate threads are virtually load-free. This uneven threadloading, of course, brings about uneven thread wear and, in the extremecase, could cause progressive thread failure as the outermost threadsfail, followed by the next succeeding threads, until eventually and overa short period of time, all of the threads have failed causing therelease of the two parts which were formerly joined thereby.

FIG. 11 schematically illustrates the multiple nut unit 100 of myinvention, including small nut members 1 10a-l00d on jackscrew 66 withtension-torsion straps a-100h extending therefrom as shown. Nowreferring to FIG. 12 we see the virtually equal thread loading on all ofthe nuts in the FIG. 11 construction. This results from the relativelysmall number of threads in each nut.

Two factors influence nut loading and must be considered. The firstinvolves the specific mechanical fits of the multiple straps at zeroload.

All straps should exhibit. the same degree of slack from nut to bladetip attachment. lf inaccuracies in slack between the straps are keptsmall relative to the large strap elongation under load, the strain forall straps will be substantially the same Suitable slack adbe used ifrequired. Y

The second consideration is the difference in strap length due to thedifference in straps because of the unequal distances between thevarious axially spaced nuts and their common retention block at theblade tip. Because the strap overall length is large compared to thedifference between the various straps, the difference in loading whichthe straps impose on each nut is relatively small and unimportant. If itis desired to avoid this difference in loading, the tip retention pointsfor the various straps can be staggered to make all straps of the samelength.

Tension-torsion straps 110 can be made out of any suitable material,such as steel in single or multiple strands, and could also be made offiber glass, boron, or any of the exotic compositions of today. The nutsegments of segmented nut 100 are preferably made of a good wearresistant material, such as beryllium copper, but other metals andcomposites could also suffice. jackscrew 66 is preferably made of steelor titanium.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person'skilled in the art.

I claim:

1. A variable length blade having a feathering axis and a blade tip endand including:

a. an inner blade portion,

b. an outer blade portion mounted for telescopic action with respect tosaid inner blade portion,

c. means to cause said outer and inner blade portions to telescope withrespect to one another including:

1. a threaded jackshaftlocated within said inner blade portion and beingfixed except for rotation with respect to said inner blade portions,

2. a plurality of nut members threadably engaging said jackshaft,

d. elongated tension-torsion straps connecting each of said nut membersto said outer blade portion.

2. Apparatus according to claim 1 and including means to cause saidjackscrew to rotate and hence vary the position of the outer bladeportion with respect to the position of the inner blade portion tothereby vary blade length.

3. Apparatus according to claim 2 wherein said jackscrew rotating meansconstitutes means-to causesaid jackscrew to rotate in either direction.

4. Apparatus according to claim 1 wherein said tension-torsion strapsconnect to said blade outer portion at the blade tip end.

5. Apparatus according to claim 1 and wherein said jackshaft isconcentric with respect to said inner and outer blade portions. 1

6. Apparatus according to claim 1 wherein said straps are of selectedlength and physical properties to distort under blade centrifugalloading sufficiently to substantially equally load each of said nuts.

7. Apparatus according to claim 1 wherein said blade portions aremounted for pitch change motion about said feathering axis and includingmeans to cause said blade portions to change pitch about the bladefeathering axis without causing motion of said nut members on saidjackshaft.

8. A variable length blade including:

a. an inner blade portion,

b. an outer blade portion mounted for telescopic mow tion relative tothe inner portion,

c. means to cause said outer and inner blade portions 'to telescope withrespect to one another including:

1. a jackscrew internal to the blade mounted for rotation, I

2. a plurality of nut members engaging said jackscrew and adapted tocontact the inner wall of the inner blade portion after a predetermineddegree of relative angular movement,

3. a plurality of tension-torsion members individually connecting saidnut members to the outer blade portion. 9. A variable length bladehaving a blade tip and in- 5 cluding:

a. an inner blade portion,

b. an outer blade portion supported from said inner blade portion forthereto, a

0. means tocause said outer blade portion to telescope with respect tosaid inner blade portion including: I

l. a jackscrew concentrically located within the interior of said innerblade portion and being mounted to be fixed with respect to said innerblade portion except for its own rotary motion,

2. a plurality of substantially equally sized nuts threadably engagingsaid jackscrew,

3. a plurality of elongated tension-torsion straps ex- I tending betweenand connected to each of said nuts and said outer blade portion.

10. Apparatus according to claim 9 wherein said blade portions aremounted for feathering action about the blade feathering axis andincluding means to cause said blade portions to move about said bladefeathering axis to vary blade pitch without causing said nuts to rotateon said jackshaft. I

11. Apparatus according to claim 11 wherein said inner blade portion ishollow and of substantially elongated cross-section, and wherein saidnuts are also shaped to be elongated in the same direction as theelongation of said inner blade portion so that during pitch changemotion said blade portion can rotate a preselected angular amountrelative to said nuts and, further, wherein as said jackscrew is causedto rotate to thereby cause said outer blade portion to telescope withrespect to said inner blade portion, said nuts abut the inner wall ofsaid inner blade portion to prevent rotation of said nuts. I

12. Apparatus according to claim 9 and wherein said nuts are of thewing-nut variety and are staggered with respect to one another on saidjackshaft so that the wings of each of said nuts are out-of-alignmentwith the wings of the remainder of the nuts'arid so that saidtension-torsion straps extend interference-free from the wings ofeachnut to the bi-ade outer portion.

13. Apparatus according to claim 9 wherein said nuts are pinned togetherto prevent relative rotation therebetween while permitting simultaneoustranslation of all nuts along said jackshaft and relative translatorymotion between said nuts along said jackshaft.

14. Apparatus according to claim 9 and including positive stop means tolimit the amount of rotation of said nuts within said inner bladeportion.

15. Apparatus according to claim 9 wherein said inner blade portion isof elliptical shape and wherein said nuts are of elliptical shape andpositioned within said inner blade position so that said inner bladeportion is capable of limited relative rotation with respect to saidnuts and wherein said nuts abut said inner blade portion to preventrotation of said nuts with said jackshaft.

16. Apparatus according to claim 9 including means to limit the endtravel of said outer blade portion with respect to said inner bladeportion.

17. Apparatus according to claim 9 wherein said tension-torsion strapsare flat members and wherein said telescoping motion with respect nutsare of the wing-nut variety and wherein one end of each tension-torsionstrap connects to one of the wings of one of said nuts, and includingbolt means connecting the end of the strap to the nut wing.

18. Apparatus according to claim 17 wherein the wings of each nutinclude an arcuate surface, and including bolt means connecting a strapend to the nut wing at a station on the wing away from the blade tip sothat the strap engages and is supported by said wing arcuate surface.

19, Apparatus according to claim 9 wherein said nuts are identical inshape and positioned in alignment on said jackscrew and include aplurality of aligned holes through said nuts, and further wherein saidtensiontorsion straps are wires with each strap extending through aseries of aligned nut holes, and further including a plate memberconnected to the blade outer portion at the blade tip and including aplurality of holes therethrough in substantial alignment with thealigned holes of the nuts and wherein said straps pass through saidholes of said plate member, and still further including means to connecteach of said straps to said plate member and one of said nuts.

20. A variable diameter rotor including:

a. a plurality of equally spaced blades mounted for rotation about anaxis of rotation,

b. each of said blades including:

1. an inner blade portion,

2. an outer blade portion mounted for telescoping motion with respect tosaid inner blade portion,

3. means to cause said outer blade portion to telescope with respect tosaid inner blade portion including:

A. a jackscrew member mounted for rotation within said inner blademember,

- B. a plurality of substantially equal sized nuts threadably engagingsaid jackscrew member,

C. a plurality of tension-torsion straps extending between and connectedto each of said nuts and said outer blade portion.

21. Apparatus according to claim 20 wherein the number of threads oneach of said nuts is small in comparison to the number of threads insaid jackscrew.

22. Apparatus according to claim 21 wherein each of said nuts has anequal number of threads.

23. Apparatus according to claim 20 wherein said torsion straps are rodmembers having a fixed head at one end thereof and an adjustable head atthe opposite end thereof and including:

a. a series of aligned drilled holes extending through said nuts,

b. a plate member attached to said outer blade portion at the blade tipand including drilled holes passing therethrough in alignment with saidaligned drilled holes and wherein said straps extend through saidaligned drilled holes of said nuts and said plate member and areretained therein by the coaction between said fixed and adjustable headsof the straps, said nuts and said plate member to thereby form aconnection between the nuts and the blade outer portion through saidstraps.

3 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Io.3,768,923 Dated October 30,1973

Inventor(s) Evan Albem Fradenburgh It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Claim 11, line 1 Delete "11'' and insert --lO-- Signed and sealed this2nd day of April 197L (SEAL) Attest:

EDWARD M.FLETCHER,JR. c. MARSHALL DANN Attesting Officer Commissioner ofPaten'

1. A variable length blade having a feathering axis and a blade tip endand including: a. an inner blade portion, b. an outer blade portionmounted for telescopic action with respect to said inner blade portion,c. means to cause said outer and inner blade portions to telescope withrespect to one another including:
 1. a threaded jackshaft located withinsaid inner blade portion and being fixed except for rotation withrespect to said inner blade portions,
 2. a plurality of nut membersthreadably engaging said jackshaft, d. elongated tension-torsion strapsconnecting each of said nut members to said outer blade portion.
 2. aplurality of nut members threadably engaging said jackshaft, d.elongated tension-torsion straps connecting each of said nut members tosaid outer blade portion.
 2. Apparatus according to claim 1 andincluding means to cause said jackscrew to rotate and hence vary theposition of the outer blade portion with respect to the position of theinner blade portion to thereby vary blade length.
 2. a plurality ofsubstantially equally sized nuts threadably engaging said jackscrew, 2.an outer blade portion mounted for telescoping motion with respect tosaid inner blade portion,
 2. a plurality of nut members engaging saidjackscrew and adapted to contact the inner wall of the inner bladeportion after a predetermined degree of relative angular movement,
 3. aplurality of tension-torsion members individually connecting said nutmembers to the outer blade portion.
 3. means to cause said outer bladeportion to telescope with respect to said inner blade portion including:A. a jackscrew member mounted for rotation within said inner blademember, B. a plurality of substantially equal sized nuts threadablyengaging said jackscrew member, C. a plurality of tension-torsion strapsextending between and connected to each of said nuts and said outerblade portion.
 3. a plurality of elongated tension-torsion strapsextending between and connected to each of said nuts and said outerblade portion.
 3. Apparatus according to claim 2 wherein said jackscrewrotating means constitutes means to cause said jackscrew to rotate ineither direction.
 4. Apparatus according to claim 1 wherein saidtension-torsion straps connect to said blade outer portion at the bladetip end.
 5. Apparatus according to claim 1 and wherein said jackshaft isconcentric with respect to said inner and outer blade portions. 6.Apparatus according to claim 1 wherein said straps are of selectedlength and physical properties to distort under blade centrifugalloading sufficiently to substantially equally load each of said nuts. 7.Apparatus according to claim 1 wherein said blade portions are mountedfor pitch change motion about said feathering axis and including meansto cause said blade portions to change pitch about the blade featheringaxis without causing motion of said nut members on said jackshaft.
 8. Avariable length blade including: a. an inner blade portion, b. an outerblade portion mounted for telescopic motion relative to the innerportion, c. means to cause said outer and inner blade portions totelescope with respect to one another including:
 9. A variable lengThblade having a blade tip and including: a. an inner blade portion, b. anouter blade portion supported from said inner blade portion fortelescoping motion with respect thereto, c. means to cause said outerblade portion to telescope with respect to said inner blade portionincluding:
 10. Apparatus according to claim 9 wherein said bladeportions are mounted for feathering action about the blade featheringaxis and including means to cause said blade portions to move about saidblade feathering axis to vary blade pitch without causing said nuts torotate on said jackshaft.
 11. Apparatus according to claim 11 whereinsaid inner blade portion is hollow and of substantially elongatedcross-section, and wherein said nuts are also shaped to be elongated inthe same direction as the elongation of said inner blade portion so thatduring pitch change motion said blade portion can rotate a preselectedangular amount relative to said nuts and, further, wherein as saidjackscrew is caused to rotate to thereby cause said outer blade portionto telescope with respect to said inner blade portion, said nuts abutthe inner wall of said inner blade portion to prevent rotation of saidnuts.
 12. Apparatus according to claim 9 and wherein said nuts are ofthe wing-nut variety and are staggered with respect to one another onsaid jackshaft so that the wings of each of said nuts areout-of-alignment with the wings of the remainder of the nuts and so thatsaid tension-torsion straps extend interference-free from the wings ofeach nut to the blade outer portion.
 13. Apparatus according to claim 9wherein said nuts are pinned together to prevent relative rotationtherebetween while permitting simultaneous translation of all nuts alongsaid jackshaft and relative translatory motion between said nuts alongsaid jackshaft.
 14. Apparatus according to claim 9 and includingpositive stop means to limit the amount of rotation of said nuts withinsaid inner blade portion.
 15. Apparatus according to claim 9 whereinsaid inner blade portion is of elliptical shape and wherein said nutsare of elliptical shape and positioned within said inner blade positionso that said inner blade portion is capable of limited relative rotationwith respect to said nuts and wherein said nuts abut said inner bladeportion to prevent rotation of said nuts with said jackshaft. 16.Apparatus according to claim 9 including means to limit the end travelof said outer blade portion with respect to said inner blade portion.17. Apparatus according to claim 9 wherein said tension-torsion strapsare flat members and wherein said nuts are of the wing-nut variety andwherein one end of each tension-torsion strap connects to one of thewings of one of said nuts, and including bolt means connecting the endof the strap to the nut wing.
 18. Apparatus according to claim 17wherein the wings of each nut include an arcuate surface, and includingbolt means connecting a strap end to the nut wing at a station on thewing away from the blade tip so that the strap engages and is supportedby said wing arcuate surface.
 19. Apparatus according to claim 9 whereinsaid nuts are identical in shape and positioned in alignment on saidjackscrew and include a plurality of aligned holes through said nuts,and further wherein said tension-torsion straps are wires with eachstrap extending through a series of aligned nut holes, and furtherincluding a plate member connected to the blade outer portion at theblade tip and including a plurality of holes therethrough in substantIalalignment with the aligned holes of the nuts and wherein said strapspass through said holes of said plate member, and still furtherincluding means to connect each of said straps to said plate member andone of said nuts.
 20. A variable diameter rotor including: a. aplurality of equally spaced blades mounted for rotation about an axis ofrotation, b. each of said blades including:
 21. Apparatus according toclaim 20 wherein the number of threads on each of said nuts is small incomparison to the number of threads in said jackscrew.
 22. Apparatusaccording to claim 21 wherein each of said nuts has an equal number ofthreads.
 23. Apparatus according to claim 20 wherein said torsion strapsare rod members having a fixed head at one end thereof and an adjustablehead at the opposite end thereof and including: a. a series of aligneddrilled holes extending through said nuts, b. a plate member attached tosaid outer blade portion at the blade tip and including drilled holespassing therethrough in alignment with said aligned drilled holes andwherein said straps extend through said aligned drilled holes of saidnuts and said plate member and are retained therein by the coactionbetween said fixed and adjustable heads of the straps, said nuts andsaid plate member to thereby form a connection between the nuts and theblade outer portion through said straps.